For the record, I have a 3" K6S.
For a 4" target gun, it really depends on which model Colt. Python > King Cobra Target. But I've heard that the grips on both could be improved for a range piece. The King Cobra Target is a closer direct comparison to the Kimber K6S, but the Python would be considerably better in every metric of performance.
I thoroughly enjoy my 3" Kimber K6S DAO, but finding larger, more hand-filling grips can be problematic. The Comfort Core grips are okay, and the Hogue Bantams feel a little better, but there is no huge squishy grip for the Kimber frame like there is for the Colts. The DAO mechanism is smooth and crisp, which makes me wonder about the DASA models, but the hammer would poke me IWB.
Another nice option, IMO, would be a Ruger Match Champion. Great sights, robust mechanism, and with the polished improvements given to that model I consider it to be on par with my S&W L-frame, but stronger. I would still guess the Python to be superior, if you could find one.